imitate this slow movement by selecting a fairly low shear rate. This low shear rate viscosity is very important and a vital point during tablet production - the lower viscosity, the better flow. You require a rheological method that, by making one set of measurements, is going to provide sufficient information to define the type of critical chocolate speed that is needed to link to shell thickness formation during shell moulding. It also needs to imply feet forming properties, chocolate ability to flow into a specific mould design, chocolate depositing and chip forming as well as air release. As an example, it is possible to demonstrate how two milk chocolates containing 29.8% and 34.8% total fat can still work in very different ways during moulding and enrobing production, despite having an identical single-speed viscosity at shear rate 7.0 [1/S]. In Figure 1, across, the low fat 29.8% milk chocolates seem to distribute itself better into the various moulds compared to the 34.8% milk chocolate, even though they both have same single-speed viscosity. Hence, these viscosity results do not show the actual difference in moulding performance. Enrobing behaviours Other forming processes such as enrobing consist of more critical chocolate speeds and is therefore a combination of different sets of flow behaviours that must be observed. In one example (Figure 2), using the same 34.8 and 29.8% milk chocolates as the moulding example above, Granola bars are enrobed under exactly the same enrobing conditions - same belt speed, curtain and blowing conditions and similar cooling. However, the low fat, 29.8% milk chocolate coats the bars with 15.6g chocolate while the 34.8% milk chocolate coats the bars with Figure 1: Differences in moulding performance using 29.8% vs. 34.8% chocolate despite similar single-speed viscosity at shear rate 7.0 [1/S] 29.8% total fat 34.8% total fat Table 3: Viscosity data of the 29.8% and 34.8% total fat chocolates. Milk chocolate Moulding viscosity shear rate 0.54[1/S] 64000 mPas 132000 mPas Spin/pump viscosity shear rate 7.0[1/S] 9800 mPas 10000 mPas Enrobing viscosity shear rate 25.0[1/S] 10200 mPas 5500 mPas 29.8% total fat 34.8% total fat 11.9g chocolate even though both milk chocolates have same singlespeed viscosity. This shows that the single-speed viscosity information does not conform to the enrobing production results. If they did the chocolate pick up should have been the same. The enrobing viscosity (high shear viscosity) is relevant to know when layer thickness is formed by blowing excess chocolate away. After enrobing, it is possible to evaluate if the proper and expected chocolate layer is obtained as calculated and designed (weight control). During passages of the enrobing curtain, the chocolate shear rate is medium and covers Swiss rolls in a relative thick layer of chocolate. After the enrobing curtain, the chocolate layer thickness is formed by the relative high shear rate Figure 2: Variations in coating of Granola bars using 29.8% and 34.8% fat milk chocolates despite both chocolates having same single-speed viscosity. Palsgaard Technical Paper - January 2012 The importance of expanded rheology information and emulsifier functionality in chocolate production 3
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